This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 2003-38378, filed on Jun. 13, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to an electrolytic condenser used in a power receiving terminal of various types of electronic apparatuses, and more particularly, to a method and apparatus for converting a voltage using an electrolytic condenser.
2. Description of the Related Art
Generally, all electronic apparatuses include a power receiving terminal to receive external power. As needed, an alternating voltage received by a power receiving terminal (hereinafter, referred to as an input alternating voltage) is converted into a direct voltage (hereinafter, referred to as an output direct voltage). To achieve this, a conventional voltage converting apparatus, such as the power receiving terminal, includes a bridge diode which full-wave rectifies an input alternating voltage and a large electrolytic condenser which charges the full-wave rectified voltage and outputs the charged voltage as an output direct voltage. To prevent explosion of the large electrolytic condenser due to an input alternating voltage of an excessive level, the conventional voltage converting apparatus includes a Zener diode (ZD) installed parallel to the large electrolytic condenser and a fuse installed at the input of the bridge diode. When the large electrolytic condenser receives an input alternating voltage that has a predetermined level or a level greater than the predetermined level which does not exceed a reverse bias voltage of the ZD, the ZD continuously clamps the input alternating voltage so as not to exceed the withstanding of the large electrolytic condenser, thereby protecting the large electrolytic condenser. When the large electrolytic condenser receives an input alternating voltage of an excessive level exceeding the reverse bias voltage of the ZD, the ZD melts and cuts off the fuse while being broken down to a short-circuit state, thereby preventing explosion of the large electrolytic condenser.
Because the conventional voltage converting apparatus cuts off the fuse in order to protect the large electrolytic condenser, repair costs are generated. After the fuse is cut off, even if an input alternating voltage with a normal level is applied, an output direct voltage is not immediately produced from the input alternating voltage until the cut-off fuse is recovered to its original state.
Also, the conventional voltage converting apparatus devises a measure to reduce an inrush current introduced into the large electrolytic condenser. A conventional voltage converting apparatus with such a measure is disclosed in FIG. 1.7.2 at page 10 of “Handbook of Switchmode Power Supplies”, written by Keith H. Billings and published by McGraw-Hill Publishing Company in 1989, which is incorporated herein by reference. The disclosed conventional voltage converting apparatus restricts the level of current rushing in a large electrolytic condenser by using a resistance R1 when an input alternating voltage starts being applied. After normally receiving the input alternating voltage, the disclosed conventional voltage converting apparatus turns on a triac by using voltages generated at both ends of a transformer T1 and restricts the level of a current rushing in the large electrolytic condenser.
The level of a sinusoidal input alternating voltage is maximum when its phase is 90° or 270°, and minimum when its phase is 0° or 180°. Nevertheless, because the conventional voltage converting apparatus restricts an inrush current regardless of the phase of the input alternating voltage, it may generate an excessive level of inrush current when the phase of the input alternating voltage is 90° or 270°. Also, the conventional voltage converting apparatus cannot completely remove the inrush current.